Heat exchangers and the method of making same



March 1969 s. F. PASTERNAK HEAT EXCHANGERS AND THE METHOD OF MAKING SAME Filed Sept. 1, 1966 INVENTOR.

3,433,300 HEAT EXCHANGERS AND THE METHOD OF MAKING SAME Stephen F. Pasternak, Park Ridge, 11]., assignor to Peerless of America, Incorporated, Chicago, Ill., a corporation of Illinois Filed Sept. 1, 1966, Ser. No. 576,599 US. Cl. 165151 10 Claims Int. Cl. F28f 1/24; F28d 21/00 ABSTRACT OF THE DISCLOSURE Heat exchangers of the side-entry cross fin type wherein the fin slots havesmall entry portions opening into the tube accommodating portions thereof.

This invention relates to a heat exchanger and a primary object is to afford a novel fin and tube heat exchanger.

Another object of the present invention is to enable a novel heat exchanger of the cross-fin type to be afforded in a novel and expeditious manner.

Heretofore, the cross-fin type of heat exchangers commonly used in the refrigeration and air conditioning fields have been of two types, namely, the plate-fin type and the side-entry type. In the plate-fin type of heat exchangers, the tubing forming the coil portion of the heat exchangers has been inserted longitudinally through openings formed in the cross-fins of the heat exchanger in inwardly spaced relation to the marginal edges thereof. The tubing in such heat exchangers is normally disposed in a serpentine pattern with substantially straight parallel passes of the tubing interconnected at their ends by return bends. Commonly, the return bends of such heat exchangers are soldered to the ends of the respective passes interconnected thereby. In this type of heat exchanger, the openings in which the tubing is mounted may have a continuous side wall, so that the tubing mounted therein may be connected to, or engaged with the fin along the entire outer periphery of the tubing.

In the aforementioned side-entry type of heat exchangers, the cross fins thereof have slots formed in the marginal edge portions thereof and the tubing is inserted transversely into the slots. With such construction, of course, tubing inserted into the slots cannot have contact with the cross fins throughout the entire outer periphery of the tubing, the peripheral contact being reduced at least by the width of the slot through which the tubing is inserted into the fins. Heretofore, it has been common practice in the manufacture of side-entry type heat exchangers to form the aforementioned slots with an entry portion leading into a body portion, and with the entry portion smaller in width than the body portion, so that the tubing may be inserted transversely through the entry portion into the body portion, and then expanded. Such expansion of the tubing serves two purposes, namely, to interlock the cross fins and tubing against removal from each other, and to engage the tubing with the side walls of the body portions.

In the plate-fin type of heat exchangers heretofore known in the art, it has been common practice to expand the tubing thereof into engagement with the side walls in the openings of the cross-fins by the application of internal pressure to the interior of the tubing.

Heretofore, the plate-fin type of heat exchanger has been the more efficient of the two types. In the plate-fin type of heat exchanger, the tubing affording the coil thereof is inserted longitudinally into openings in the plate-fins. With this construction, the tubing and the openings in the fins may be of such size that in the assemnited States Patent f 3,433,300 Patented Mar. 18, 1969 bly of the heat exchanger they may be forced together with a force fit, or, after being installed in the openings the tubing may be expanded into firm engagement with the side walls of the openings. With the plate-fin type of heat exchanger wherein the opening for each pass has a continuous side wall, engagement may be afforded between the tubing and the side walls of the openings in the cross-fins throughout the entire outer periphery of the tubing, so as to afford good heat transfer between the tubing and the cross-fins.

Of course, in a side-entry heat exchanger, such contact between the cross-fins and the entire outer periphery of the tubing is impossible. In this latter type of heat exchanger, the tubing is moved transversely through the open ends of outwardly opening slots formed in the marginal edge portions of the cross-fins into the closed ends thereof. With such construction, the peripheral contact of the tubing with the cross-fins can never be greater than the periphery of the tubing minus the width of the entry opening of the slots. Heretofore, the width of the entry portion of the slot-s has commonly been a substantial portion of the periphery of the tubing.

In an attempt to eliminate as much of the aforementioned lost contact between the cross-fins and the tubular members as possible, the slots in the aforementioned sideentry type heat exchangers heretofore known in the art have commonly been constructed with narrower entry portions extending from the marginal edge of the fin into enlarged body portions. In certain instances, in sideentry type heat exchangers heretofore known in the art, tubes having such a normal outside diameter that they may be inserted transversely through the entry portion into the body portion of the slots have been used, the tubes being expanded beyond their normal size into engagement with the side walls of the body portion after insertion thereinto. In other instances, tubes have been deformed in a direction to permit entry through the entry portions of such slots heretofore known in the art and, after insertion through the entry portion into the body portion have been expanded back into their normal shape, or into an enlarged shape and size, so as to engage the side Walls of the aforementioned body portions and interlock the tubes and cross-fins against transverse removal of the tubing from the cross-fins.

One of the problem heretofore present in the art with respect to side-entry heat exchangers has been that the entry portion of the slots thereof has had to be of such size that even after the tubing has been expanded in the body portion of the slots, the opening afforded between the entry portion and the body portion is of sufficient size that the heat transfer between the tube and the fin is substantially less than the heat transfer between a tube of the same size and a plate fin mounted thereon, wherein the plate fin has openings embodying the aforementioned continuous side Walls. It is an important object of the present invention to enable the disparity between the heat transfer afforded by plate fins and side-entry fins heretofore known in the art to be reduced to a substantially negligible amount.

In the manufacture of heat exchangers both of the plate fin and side-entry type, it heretofore has been common practice to expand the tubing by the application of internal pressure thereinto after the fins have been mounted thereon, in an endeavor to afford firm contact between the tubing and the entire length of the side wall of the opening in which the tubing is disposed. As will be appreciated by those skilled in the art, if sutficiently firm engagement between such tubing and the entire side wall of the opening in a fin is afforded, effective heat transfer may be afforded between the tubing and the fin without the necessity of soldering or otherwise connecting the fin to the tubing.

In plate-fin type heat exchangers, such firm engagement between the tubing and the cross fins is quite readily afforded when the outside diameter of the tubing and the diameter of the opening through which it is inserted are such that a snug initial fit is afforded, it merely being necessary to expand the tubing a slight additional amount to afford such firm engagement. Such slight additional expansion may be relatively readily accomplished by the application of internal pressure into the tubing. However, plate fins embodying round opening having a continuous side Wall portion have several inherent disadvantages, such as, for example, being somewhat difiicult to assemble; and being impossible to fabricate using a continu ous integral serpentine tube, it being necessary to solder, or otherwise connect, the return bends to the passes of the tubes extending through the fin after the fins have been mounted on the passes.

Heretofore, in the manufacture of plate-fin heat exchangers of the aforementioned type, it has been common to use copper tubing, so that it has been a relatively simple matter to solder the return bends to the passes of the .coil, although it did require an additional step. In recent years, copper tubing has become increasingly difficult to obtain, and it has been discovered that other types of tubing, such as, for example, aluminum have certain advantages over copper tubing and are more readily available on the market. However, aluminum tubing is relatively difiicult to solder, and, particularly, on a commercial production-line basis. Therefore, with the advent of the increased use of aluminum tubing in heat exchangers of the aforementioned type, it has become increasingly difficult to assemble such heat exchangers when they embody the aforementioned plate-type cross fins It is another important object of the present invention to enable aluminum tubing to be used in cross-fin type heat exchangers in a novel and expeditious manner.

By using side-entry type cross fins, heat exchangers wherein the tubing thereof constituted a single, integral piece of tube have heretofore been able to be afforded. Such construction lends itself well to the use of aluminum tubing, it being unnecessary to solder together the various portions of the coil. However, in such side-entry construction heretofore known in the art, the width of the entry portion of the marginal slots in the cross fins has heretofore been a substantial portion of the outside diameter of the tubing to be inserted therethrough. For example, in side-entry heat exchangers wherein the tubing had an outside diameter of the entry portion of the slots in the marginal edge portions of the cross fins have commonly been in the nature of Therefore, the loss in peripheral contact between the tubing and the cross fins, because of the entrance opening of the slot, has been substantial, and the efiiciency of heat transfer between the tubing and fins of such side-entry heat exchangers has been considerably less than the efliciency of the heat transfer between the tubing and the fins of the plate-fin type heat exchanger, wherein the openings therethrough were round and continuous. It is another important object of the present invention to enable the size of the entry portion of the slots in side-entry cross fins to be substantially reduced in a novel and expeditious manner.

Another object of the present invention is to enable the disparity between the efiiciency of heat transfer between tube of the same size and fins of the plate-type and sideentry type to be reduced to a substantially negligible amount.

Heretofore, in the manufacture of side-entry type heat exchangers, it has been a common practice to use tubing having such a normal outside diameter that it could be inserted transversely through the entry portion of the slots in the marginal edge portions of the cross fins into the body portions thereof and then to expand the tubing, transversely to the longitudinal center line of the entry portion, into the enlarged body portions of the slots, by the application of external pressure, as disclosed in United 4 States Letters Patents Nos. 2,540,339 and 2,567,716 issued to R. W. Kritzer; or to first flatten the passes of the tubing, having a normal outside iameter greater than the width of the entry portion of the slots, so that the tubing may be inserted transversely through the entry portions into the body portions of the slots and, then, by the application of external pressure expand the tubing into the body portions of the slots as disclosed in United States Letters Patent No. 2,913,806, issued to R. W. Kritzer. Although these methods of fabricating side-entry type heat exchangers have been highly successful and have had much commercial success, they have certain inherent disadvantages. For example, using this method of fabricating side-entry type heat exchangers, it has normally been necessary to have the width of the entry portion of the slots be a substantial portion of the ultimate length of contact between the tubes and the side wall of the body portion of the slot in which the tube is mounted; and the external force which it is necessary to apply to the tubing in order to expand it into the body portion of the slots is substantial. This has heretofore meant that either the fin strength had to be suflicient to withstand such external forces, or the adjacent fins had to be spaced apart a sufficient distance to permit a supporting member to be inserted therebetween during the application of the external forces necessary to position the tubing in the body portion of the slots. In refrigeration coils, and the like, wherein the spacing of adjacent fins may be suficiently great to permit the insertion of combs, or like tools, therebetween for supporting the tubes during the application of the aforementioned external forces, and in heat exchanger constructions wherein the cross-fin structure had the requisite strength to Withstand the aforementioned external forces, such methods of manufacture have been highly practical and successful.

However, in certain heat exchanger units, such as, for example, in evaporators commonly used in the air conditioning field, the fins thereof have a thickness in the nature of .006", and are commonly spaced from each other at the rate of ten to sixteen fins per inch. Normally, such fin structures do not have the requisite structural strength to withstand the external forces necessary to expand the tubular members in the body portions of the slots in the aforementioned manner; and the cross fins in such units are so closely spaced that it is impractical to insert a comb or other suitable tool therebetween for withstanding the aforementioned external forces.

Other disadvantages of using the aforementioned methods of expanding tubing into the side-entry slots by the application of external forces have been that it tends t flatten at least one side of the tubing as shown in the aforementioned Kritzer patents, and thus to change the internal dimensions of the tubing; and unless the tubing is of substantial width, transversely of the application of the external forces, when the external forces are applied thereto, the forces tend to buckle rather than expand the tubing.

Another method which has heretofore been tried for expanding tubing into the body portion of side-entry slots in cross fins has been the application of internal pressure to the interior of the tubing. This method has also had several inherent disadvantages such as, for example, tending to blow out or rupture the return bends of the tubing prior to effecting full expansion of the tubing in the body portions of the slots; and failing to expand the tubing into firm engagement with the side walls of the body portions throughout the full length of the side walls. It is an important object of the present invention to enable tubing to be expanded into the body portion of side-entry slots in a novel and expeditious manner by the combined simultaneous application of external and internal pressure thereto.

Another object is to enable tubing to be expanded into firm engagement with the side walls of side-entry slots without danger of rupturing the return bends thereof.

Another object of the present invention is to enable a side-entry type heat exchanger to be afforded wherein firm contact, affording good heat transfer between the tubing and cross fins, is afforded throughout the entire length of the side wall of the body portion of each of the side-entry slots.

Heretofore, another disadvantage of the side-entry type heat exchangers has been that, as a practical matter, they were substantially limited to two-row coil units. This has been true because the entry portions of such heat exchangers heretofore known in the art have been so wide that little or no purpose would be served in affording the staggered type of coil arrangement in the cross-fins, which is necessary to afford a coil of more than two rows. In the side-entry type heat exchangers heretofore known, the entry portions of the side-entry slots were of such width that it was substantially impossible, as a practical matter, to afford a staggered-type of coil arrangement, with three or more coils, because of the loss in secondary heat transfer surface, and the loss of structural strength in the cross-fins.

It is another important object of the present invention to enable a novel side-entry type heat exchanger having three, or more, rows of coils to be afforded in a novel and expeditious manner.

Another object is to enable to be afforded a novel sideentry type heat exchanger having three, or more, rows of coils, wherein the entry portions of the adjacent slots thereof are so narrow that the loss in secondary heat transfer surface and in structural strength is substantially insignificant in comparison to plate-fin type of heat exchangers of comparable tube size and construction.

Yet another object of the present invention is to enable a novel side-entry heat exchanger to be afforded wherein the entry portion of the side-entry slots thereof is substantially smaller than the entry portion of side-entry slots heretofore known in the art.

A further object of the present invention is to enable a novel side-entry type heat exchanger to be afforded wherein the entry portion of each of the side-entry slots thereof is little greater in Width than the thickness of a tube to be mounted in the slot would be if the tube were completely flattened.

Another object of the present invention is to enable a novel heat exchanger of the aforementioned type to be afforded wherein it is unnecessary to secure the cross fins thereof to the coils thereof by soldering, or the like, in order to afford good heat transfer between the fins and tubing.

Another object of the present invention is to afford a novel side-entry type heat exchanger which is practical and efficient in operation, and which may be readily and economically produced commercially.

A further feature is to provide a particular method of making a side-entry heat exchanger, and which method is practical and efficient, and may be readily used commercially.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what I now consider to be the best mode in which I have contemplated applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a side elevational view of a heat exchanger embodying the principles of the present invention;

FIG. 2 is a fragmentary, detail sectional view, somewhat diagrammatic in form, taken substantially along the line 22 in FIG. 1;

FIG. 3 is an enlarged, fragmentary, detail sectional view taken substantially along the line 3-3 in FIG. 2;

FIG. 4 is an enlarged, fragmentary, detail sectional view of a portion of the heat exchanger shown in FIG. 2, showing the heat exchanger in an early stage of assembly;

FIG. 5 is a view similar to FIG. 4, but showing the heat exchanger in a later stage of assembly;

FIG. 6 is a view similar to FIG. 5, but showing the heat exchanger in a later stage of assembly;

FIG. 7 is a view similar to FIG. 6, but showing the heat exchanger in a later stage of assembly;

FIG. 8 is a sectional view similar to FIG. 7, but showing the heat exchanger in its completed form of assembly, as shown in FIG. 2; and

FIG. 9 is a detail sectional view similar to FIG. 2, but showing a modified form of the heat exchanger assembly.

A heat exchanger 1, embodying the principles of the present invention, is shown in FIGS. 1 to 8 of the drawings to illustrate the presently preferred embodiment of the present invention.

The heat exchanger 1 embodies, in general, a one-piece tubular coil 2 having a plurality of closely spaced cross fins 3 mounted thereon, FIG. 1. The cross fins 3 are of the side-entry type, as illustrated in FIG. 2. Each fin 3 is rectangular in shape and embodies a plurality of identical side-entry slots 4 disposed in spaced relation to each other in the respective longitudinal marginal edge portions 5 and 6 thereof, FIG. 2. Each of the slots 4 has an entry portion 7 which extends inwardly from a respective longitudinal marginal edge of the respective fins 3, and an enlarged body portion 8 in communication with the inner end of the side-entry portion 7 and extending inwardly therefrom. The slots 4 are preferably so disposed in each of the fins 3 that the entry portions 7 in each of the longitudinal edge portions 5 and 6 are disposed in parallel relation to each other, with the longitudinal center lines of the entry ortions 7 in each edge portion 5 and 6 being disposed midway between the longitudinal center lines of adjacent pairs of the entry portions 7 in the other edge portion 6 or 5.

The coil 2 may be formed of any suitable material, such as, for example, aluminum, and preferably consists of a single, unitary tubular member. It is formed into a serpentine pattern having two rows 9 and 10, FIG. 2, of passes 11. The adjacent passes 11 in each of the respective rows 9 and 10 are interconnected at their ends by return bends 12, and the lowermost passes 11 in the two rows 9 and 10 are interconnected by a return bend 13 disposed transversely to the return bends 12, FIG. 1. The upper one of the passes 11 in the row 9 extends outwardly beyond the stack of fins 3 to afford an inlet 14 for the coil 2, and the upper one of the passes 11 in the row 10 extends outwardly from the stack of fins 3 to afford an outlet 15 for the coil 2. With this construction, working fluid, such as, for example, refrigerant may be fed from a suitable source of supply, such as a compressor, not shown, into the coil 2 through the inlet 14 from which it may flow horizontally back and forth through the fins 3, as viewed in FIG. 1, downwardly from one pass 11 to the other in the row 9, across the return bend 13 to the lower pass 11 in the row 10, and then horizontally back and forth across the fins 3 upwardly through the passes 11 in the row 10 and outwardly through the outlet 15.

Flanges 16 are formed on each of the fins 3 around the body portion 8 of each of the slots 4, FIGS. 2-8, to afford reinforcing members for the body portions 8. The flanges 16 project outwardly from the planes of the body portions of each of the respective fins 3 to afford spacers between adjacent fins 3, FIG. 3. Preferably, in the assembled heat exchanger 1, the body portions of adjacent fins 3 are spaced from each other along the passes 11 of the coil 2 the thickness of the respective flanges 16, as shown in FIG. 3.

In the preferred form of the invention shown in the drawings, the shape of the body portions 8 of the slots 4 is that of an arc of a circle, and the entry portions 7, extending outwardly therefrom, are substantially straight, having parallel side walls 17 and 18 extending outwardly from the side walls 19 of the respective body portions 8.

Preferably, the radius of the arc of the body portion 8 of each of the slots 4 is the same as the normal outside radius of the tubular member affording the coil 2, and the width of each entry portion 7 of the slots 4 is substantially less than the diameter of the body portion 8 to which it is connected, as will be discussed in greater detail presently.

In making the novel heat exchanger 1 in accordance with the principles of the novel method of the present invention, the cross fins 3 are formed with the entry portions 7 of the slots 4 substantially narrower than the normal outside diameter of the tube 2, The tube 2 is then preformed into the serpentine shape of the heat exchanger 1 shown in FIG. 1, with the passes 11, between the return bends 12 at the opposite ends thereof, flattened to such a thickness that they may be inserted transversely through the entry portions 7 of the slots 4 into the body portions 8 thereof, into the position shown in FIG. 4. In this position of the passes 11, the edge portions 20 thereof, herein referred to as the leading edge portions, are disposed in abutting engagement with the portions of the side walls 19 of the respective body portions 8, which are disposed on the side of the respective entry portions 7 remote from the respective marginal edges 5 and 6 of the fins 3. Also, in such position of the passes 11, the edge portions 21 thereof, herein referred to as the trailing edge portions, project outwardly through the entry portions 7 of the respective slots 4.

With the coil 2 thus disposed in the slots 4 in the fins 3, it may be simultaneously subjected to internal pressure and external pressure suflicient to expand the passes 11 thereof from a flattened shape, such as shown in FIG. 4, to a substantially round shape, such as shown in FIG. 8, wherein they completely fill the body portion 8 of the respective slots 4. To accomplish this, the ends 14 and of the coil 2 may be connected to a suitable source of pressurized working fluid, not shown, such as, for example, a suitable source of hydraulic fluid; and the heat exchanger 1 may be mounted in a suitable press, or the like, wherein dies, such as the dies D and D FIG. 2, may be abuttingly engaged with the trailing edge portions 21 of the passes 11 in the rows 9 and 1%, respectively, in position to exert the aforementioned external force on the passes 11 at the opposite sides of the fins 3.

As the aforementioned internal and external pressure is applied to the coil 2, the passes 11 are caused thereby to expand from the flattened shape shown in FIG. 4 to the full expanded shape shown in FIG. 8. During this time, the dies D and D preferably continuously move inwardly toward each other in such a manner as to continuously clamp the coil 2 therebetween with sufficient force to maintain the leading edge portions of the passes 11 in engagement with the portions of the side walls 19 of the respective body portions 8 disposed directly opposite the respective entry portions 7. The application of the aforementioned external force serves three main functions. The first of these functions is that by thus holding the leading edge portions 20 of the passes 11 in engagement with the adjacent portions of the side walls 19 of the respective body portions 8, it prevents these portions 20 of the passes 11 from pulling away from the side walls 19, which they tend to do if the coil 2 is expanded only by internal pressure. This maintaining of engagement between the leading edges 20 of the passes 11 and the side walls 19 of the body portions 8 assists in insuring that when expansion of the passes 11 is completed, the passes 11 will be in finm engagement with the side walls 19 throughout the length of the latter.

The second function of the aforementioned external forces is that the external force thus applied to the trailing edge portions 21 of the passes 11, itself, tends to expand the passes 11 and thereby assists the expansion efforts of the internal pressure applied to the passes 11 of the coil 2. Heretofore, it has been found that when internal pressure, alone, has been utilized in an attempt to expand the passes of serpentine tubing, such as that embodied in the heat exchanger 1, there has been substantial danger of rupturing, or blowing out, the return bends connected to the passes. In fact, the problem has proven to be so acute as to render such method of expansion of passes, such as the passes 11, substantially useless as a practical method of expanding such passes commercially. It has been found that with the application of the aforementioned external force simultaneously with the application of such internal force, in accordance with the principles of the present invention, a practical, highly effective method of expanding such passes in commercial operations is afforded; and that the external forces thus applied may be suificiently small that they do not objectionably, permanently deform the fins 3.

The third function of the aforementioned external forces applied to the passes 11 is to move the trailing edge portions 21 thereof inwardly through the respective entry portions 7 at a rate wherein, during expansion of the passes 11 in the body portions 8, the side walls of the expanding passes 11 are maintained out of engagement with the side walls 17 and 1 8 of the entry portions 7, and out of engagement with the junction of the side walls 17 and 18 with the side walls 19 of the respective body portions 8. During the expansion of the passes 11 under the internal and external forces preferably applied in the practice of the present invention, they progressively enlarge from the inner side of the body portions 8 toward the respective entry portion 7, as illustrated in FIGS. 4-8, with the trailing edge portions 21 moving inwardly to a position wherein the passes 11 are again substantially round when the expansion thereof is completed, FIG. 8. Such progressive expansion of the passes 11 prevents them from applying undesirable expanding and tearing forces to the side walls of the slots 4. Also, it assists in insuring a substantially round cross-section for the fully expanded passes.

I prefer initially to flatten the passes 11 to the somewhat tear-drop shaped cross section shown in FIG. 4, wherein the leading edge poition 20 is somewhat thicker than the trailing edge portion 21, so as to assist in the aforementioned progressive expansion of the passes 11 during the application of the internal and external expansion forces thereon. However, as will be appreciated by those skilled in the art, this merely represents the preferred embodiment of my invention, and other cross-sectional shapes may be used by those skilled in the art without departing from the purview of the present invention.

Preferably, the external forces applied to the trailing edges 21 of the passes 11 on the opposite sides of the fins 3 are sufliciently small that they will not cause buckling or permanent distortion of the fins 3, but are sufliciently large as to serve the aforementioned functions.

With this method of manufacturing heat exchangers, such as the heat exchanger 1, it has been found that tubular members which have been flattened to substantially completely flat condition may be expanded to their normal round position in side-entry slots, such as the slots 4, by the use of a combination of internal pressure which is substantially below the pressure necessary to rupture any portion of the coil 2, and an external clamping force, which is substantially below the force necessary to buckle or permanently deform the fins 3, which are made from relative thin and structurally weak material. For example, in the practice of the present invention, using a tube having an outside diameter of and a wall thickness of .035" for the coil and using fins having a thickness of .006", with the fins disposed on the coil 2 at the rate of fourteen fins per inch, and with the body portions 8 of the slots 4 and 5 having a diameter of the passes 11 may be flattened initially to such an extent that they may be inserted through entry portions 7 having a width of not more than .14, and expanded into the body portion 8 into substantially round shape wherein they have again assumed their original outside diameter of /8", or slightly more, so as to firmly engage the side walls 19 of the body portions 8 throughout the length of the side walls 19. It has been found that this may be accomplished with an internal expansion pressure well below the pressure necessary to rupture the coil 2, and with an external force well below that necessary to buckle or permanently deform the fins 3.

Furthermore, it has been found that using this novel method of making a heat exchanger, the passes 11 may be so firmly engaged with the side walls 19 of the body portions 8 of the side-entry slots 4 that the fins 3 are securely held by this engagement, alone, in position on the coil 2, and effective heat-transfer engagement is afforded between the outer periphery of the passes 11 and the entire length of the side walls 19 of the body portions '8. With the heat exchanger 1 constructed in this manner, it is unnecessary to afford an additional securing of the cross fins 3 to the coil 2, such as, for example by solder.

As will be appreciated by those skilled in the art, a heat exchanger embodying the principles of the present invention, and the method of making such a heat exchanger, as disclosed herein, is far different from anything heretofore known in the art. Heretofore, it has been common practice in the manufacture of side-entry type heat exchangers to make the width of entry portions of the slots a minimum of seventy-five to eighty percent of the normal outside diameter of the tube being inserted therethrough. Thus, for example, it has been common practice in such heat exchangers, wherein the outside diameter of the tube is in the nature of to have the width of the entry portion of the side-entry slot be With such construction, the lack of contact between the side entry fins and the coil on which they are mounted afforded by the entry portion thereof has been sufiicient that the heat transfer between the coil and the fins has been several percentage points less than that in heat exchangers of the plate-fin type having the same tube and fin sizes. However, using the method of manufacture embodying the principles of the present invention, and affording a side-entry heat exchanger embodying the principles of the present invention, it has been found that this disparity in heat transfer between side-entry type and plate-fin type heat exchangers may be reduced to the relatively negligible amount of less than one percent.

One of the main purposes of the present invention is to afford such increased efiiciency of sideentry type heat exchangers, and to eliminate the necessity for having the entry portion of side-entry slots be of such relatively great width. It has been found that, using the principles of the present invention, and with tubing having the usual ratio of wall thickness to outside diameter, such as, for example, .035" to the side-entry portion 7 of the slots 4 may constitute not substantially more than twenty percent of the diameter of the body portion 8 thereof, and, in some instances may be less than the aforementioned twenty percent.

As will be appreciated by those skilled in the art, the extent to which a tubular member may be flattened and again expanded to its original round shape, and, therefore, the width of the entry portion of a side-entry slot through which such a tubular member may be inserted, is controlled to a certain extent by the thickness of the wall of the tubular member. Excessive flattening of a tubular member, particularly when combined with subsequent expansion thereof, may cause the tubular member to separate or rupture. However, I have found that aluminum tubing, and the like, of the type commonly used in heat exchanger units of the type with which the present invention is concerned, may be flattened to a thickness in a range of between three to five times the wall thickness of the tubing, and preferably to the thickness of four times the wall thickness of the tubing, in preforming the tubing for insertion into side-entry slots in fins in accordance with the principles of the present invention. This permits side-entry slot widths of a corre sponding size, namely, in the range of three to five times the wall thickness of the tubing, and preferably in the nature of four times such wall thickness.

In FIG. 9 a modified form of the present invention is illustrated. FIG. 9 is similar to FIG. 2, and illustrates a heat exchanger 1a which is identical to the heat exchanger shown in FIGS. 1-8, except that it embodies four rows of passes rather than the two rows of passes 14 shown in FIG. 2. In FIG. 9, parts which are the same as parts shown in FIGS. 18 are indicated by the same reference numerals, and parts which have been substituted for parts shown in FIGS. 1-8 are indicated by the same reference numerals with the sufiix a added thereto.

In the heat exchanger 1a shown in FIG. 9, two rows 9 and 10 of passes 11 are mounted in fins 3a in side-entry slots 4 which are identical to the slots 4 shown in FIG. 2. In addition, two other rows 9a and 10a of passes 11 are mounted in side-entry slots 4a. The slots 4a are identical in construction to the slots 4, except that the entry portions 7a thereof are longer than the entry portions 7 so that the body portions 8a of the slots 4a are disposed a greater distance from the respective marginal edges 5 and 6 of the fins 3a. The slots 4 and 4a are so disposed in the fins 3a that each slot 4 is disposed in axial alignment with slot 4a formed in the opposite longitudinal edge portion 5 or 6 of the fins 3a. As will be observed, with this construction, a staggered arrangement of rows of passes is afforded, with the rows 9a and being disposed inwardly of the rows 9 and 10, in parallel relation thereto.

The narrow entry portions 7 of the slots 4 and 4a makes possible the affording of a practical three-row, or more, heat exchanger of the side-entry type. With the entry slots of a side-entry type heat exchanger constructed in accordance with the principles of the present invention, adjacent slots in such staggered arrangements may be spaced sufficiently close together, while retaining the desired strength and heat transfer characteristics of the marginal edge portions of the cross-fins, that a substantially greater capacity unit may be afforded by constructing a coil having more than two rows. This was not true with respect to side-entry type heat exchangers heretofore known in the art.

It will be appreciated by those skilled in the art that a greater or lesser number of rows of passes than that shown in either FIG. 2 or 9 may be afforded without departing from the purview of the present invention, and that the present invention affords particular advantages in the construction of staggered-row type heat exchangers, such as, for example, three-row heat exchangers.

In addition, the present invention affords a novel sideentry fin construction for heat exchangers.

Also, it will be seen that the present invention affords a novel side-entry heat exchanger which is practical and efficient in operation, and which may be readily and economically produced commercially.

Thus, while I have illustrated and described the preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. A heat exchanger comprising (a) a coil of tubing including (1) passes and (2) an integral return bend, and (b) cross fins having slots in the marginal edge portion thereof for the side-entry of said passes thereinto,

1 1 (c) said slots having (1) entry portions opening outwardly through said marginal edge portion of said tins, and (2) body portions disposed inwardly of said entry portions,

(d) said passes in the assembled heat exchanger being disposed in said body portions in snug fitting engagement with the side walls of said body portions throughout the length of said side walls, and

(e) said entry portions having a width at their narrowest portions of not substantially less than three times the wall thickness of said passes and not substantially more than five times the wall thickness of said passes.

2. A heat exchanger as defined in claim 1, and in (a) said entry portions have a width at their narrowest portions of not substantially more than four times said wall thickness.

3. A heat exchanger comprising (a) a coil of tubing including (1) passes and 2) an integral return bend, and

(b) cross-fins having slots in the marginal edge portions thereof for the side-entry of said passes thereinto,

(c) said slots having (1) entry portions opening outwardly through said marginal edge portions of said fins, and

(2) body portions disposed inwardly of said entry portions,

(d) said passes in the assembled heat exchanger being disposed in said body portions in snug fitting engagement with the side walls of said body portions throughout the length of said side walls, and

(e) said entry portions of respective ones of said slots having a width at their narrowest portions of less than twenty percent of the longest transverse dimension of said body portions thereof.

4. A heat exchanger comprising (a) a coil of tubing having a serpentine form and including (1) substantially straight parallel passes and (2) integral return bends, and

(b) a plurality of substantially parallel cross fins,

(c) each of said fins having slots in the marginal edge portions thereof for the side-entry of said passes thereinto,

(d) each of said slots having (1) an entry portion opening outwardly through a marginal edge of a respective fin, and

(2) a substantially circular-shaped body portion extending inwardly from said entry portion in communication therewith,

(e) said passes in the assembled heat exchanger being disposed in respective ones of said body portions in each of said fins in engagement with the side walls of said body portions throughout the length of said side walls, and

(f) said entry portion of each of said slots having a Width at the junction thereof with said respective body portion of less than eighty percent of the diameter of said body portion of said slot.

5. A heat exchanger as defined in claim 4, and in which (a) said entry portion of each of said slots has a width at said junction of not substantially more than four times the wall thickness of said pass disposed in said slot.

6. A heat exchanger as defined in claim 4, and in which (a) said entry portion of each of said slots has a width at said junction of not substantially less than three times, and not substantially more than five times, the wall thickness of said pass disposed in said slot.

7. A heat exchanger as defined in claim 4, and in which (a) said entry portion of each of said slots has a Width at said junction of not substantially more than twenty percent of the diameter of said body portion of said slot.

8. A heat exchanger comprising (a) a coil of tubing including (1) passes and (2) an integral return bend, and

(b) cross fins having slots in the marginal edge portion thereof for the side-entry of said passes thereinto,

(c) said slots having (1) entry portions opening outwardly through said marginal edge portion of said fins, and

(2) body portions disposed inwardly of said entry portions,

(d) said passes in the assembled heat exchanger being disposed in said body portions in snug fitting engagement with the side walls of said body portions throughout the length of said side walls, and

(c) said body portions of adjacent ones of said slots being disposed at diiferent distances from the outer edge of said marginal edge portion.

9. A heat exchanger as defined in claim 8, and in which (a) said entry portions have a width of less than eighty percent of the diameter of said body portions and of not substantially more than twenty percent of the diameter of said body portions.

10. A heat exchanger as defined in claim 8, and in which (a) said entry portions have a minimum width of not substantially less than three times the wall thickness of said passes and not substantially more than five times said wall thickness.

References Cited UNITED STATES PATENTS 2,823,016 2/ 1958 Greer.

2,834,583 5/1958 Oldberg et a1.

2,934,917 5/1960 Collins.

2,987,300 6/ 1961 Greene.

2,023,739 12/ 1935 Mason 182 X 2,475,187 7/1949 Kramer 165-182 X 2,540,339 2/1951 Kritzer 165182 X 3,216,095 11/1965 Kurtz et al 165181 ROBERT A. OLEARY, Primary Examiner.

THEOPHIL W. STREULE, Assistant Examiner.

U.S. Cl. X.R. 

